1. Field of the Invention
The present invention relates to data driving circuits, light emitting displays employing such data driving circuits and methods of driving the light emitting displays. More particularly, the invention relates to data driving circuits capable of displaying images with uniform brightness, a light emitting display using such a data driving circuit and methods of driving the light emitting display to display images with uniform brightness.
2. Description of Related Art
Flat panel displays (FPDs), which are generally lighter and more compact than cathode ray tubes (CRTs), are being developed. FPDs include liquid crystal displays (LCDs), field emission displays (FEDs), plasma display panels (PDPs) and light emitting displays.
Light emitting displays may display images using organic light emitting diodes (OLEDs) that generate light when electrons and holes re-combine. Light emitting displays generally have fast response times and consume relatively low amounts of power.
FIG. 1 illustrates a schematic of the structure of a known light emitting display.
As shown in FIG. 1, the light emitting display may include a pixel unit 30, a scan driver 10, a data driver 20 and a timing controller 50. The pixel unit 30 may include a plurality of pixels 40 connected to scan lines S1 to Sn and data lines D1 to Dm. The scan driver 10 may drive the scan lines S1 to Sn. The data driver 20 may drive the data lines D1 to Dm. The timing controller 50 may control the scan driver 10 and the data driver 20.
The timing controller 50 may generate data driving control signals DCS and scan driving control signals SCS based on externally supplied synchronizing signals (not shown). The data driving control signals DCS may be supplied to the data driver 20 and the scan driving control signals SCS may be supplied to the scan driver 10. The timing controller 50 may supply data DATA to the data driver 20 in accordance with externally supplied data (not shown).
The scan driver 10 may receive the scan driving control signals SCS from the timing controller 50. The scan driver 10 may generate scan signals (not shown) based on the received scan driving control signals SCS. The generated scan signals may be sequentially supplied to the pixel unit 30 via the scan lines S1 to Sn.
The data driver 20 may receive the data driving control signals DCS from the timing controller 50. The data driver 20 may generate data signals (not shown) based on the received data DATA and data driving control signals DCS. Corresponding ones of the generated data signals may be supplied to the data lines D1 to Dm in synchronization with respective ones of the scan signals being supplied to the scan lines S1 to Sn.
The pixel unit 30 may be connected to a first power source ELVDD for supplying a first voltage VDD and a second power source ELVSS for supplying a second voltage VSS to the pixels 40. The pixels 40, together with the first voltage VDD signal and the second voltage VSS signal, may control the currents that flow through respective OLEDs in accordance with the corresponding data signals. The pixels 40 may thereby generate light based on the first voltage VDD signal, the second voltage VSS signal and the data signals.
In known light emitting displays, each of the pixels 40 may include a pixel circuit including at least one transistor for selectively supplying the respective data signal and the respective scan signal for selectively turning on and turning off the respective pixel 40 of the light emitting display.
Each pixel 40 of a light emitting display is to generate light of predetermined brightness in response to various values of the respective data signals. For example, when the same data signal is applied to all the pixels 40 of the display, it is generally desired for all the pixels 40 of the display to generate the same brightness. The brightness generated by each pixel 40 is not, however, only dependent on the data signal, but is also dependent on characteristics of each pixel 40, e.g., threshold voltage of each transistor of the pixel circuit.
Generally, there are variations in threshold voltage and/or electron mobility from transistor to transistor such that different transistors have different threshold voltages and electron mobilities. The characteristics of transistors may also change over time and/or usage. For example, the threshold voltage and electron mobility of a transistor may be dependent on the on/off history of the transistor.
Therefore, in a light emitting display, the brightness generated by each pixel in response to respective data signals depends on the characteristics of the transistor(s) that may be included in the respective pixel circuit. Such variations in threshold voltage and electron mobility may prevent and/or hinder the uniformity of images being displayed. Thus, such variations in threshold voltage and electron mobility may also prevent the display of an image with a desired brightness.
Although it may be possible to at least partially compensate for differences between threshold voltages of the transistors included in the pixels by controlling the structure of the pixel circuits of the pixels 40, circuits and methods capable of compensating for the variations in electron mobility are still needed. OLEDs that are capable of displaying images with uniform brightness irrespective of variations in electron mobility are also desired.